Process of inductively heating pliers



Feb. 22, 1949. F. N. DARMARA 2,462,072

PROCESS OF INDUCTIVELY HEATING PLIERS Filed Dec. 18, 1945 INVENTOR.

W &W

ATTORNEYS.

passing through a coil 5 Patented Feb. 22, 1949 PROCESS OF INDUCTIVELY HEATING PLIERS Falih N. Darmara; Utica, N. Y., assignor to Utica 'Drop Forged; Tool Corporation, Whitestown,

N. Y., a corporation of New'York Application December 18, 1943, Serial No. 514,816

Z'Claims.

1 My present invention relates to a-process of heating the cutting edges and external surfaces of hand tools.

One purpose of my invention is to provide'a new and improved'processof heatingthe opposed cutting edges of cutting pliers and other related hand tools and the external skin of the workin portions of such hand tools and further to so heat by induced electric current such a hand tool at any stage of manufacture.

The most desirable sort of hardening procedure is one which hardens the surface of the working portions of the tool without such hardness penetrating all the way through the tool. When the hardness goes all the way through, the tool is brittle. When it goes only part way through, the soft tough center prevents the tool cracking in use. The cutting edges in hand tools being always opposed and close together are diificult to harden without hardening all the metal surrounding them. By'my process only the opposed cutting edges-and the external skin of the working portion of the tool are hardened; thus giving the ideal condition.

Referring first to the process and its metallur- "gical aspects, it will be seen that the heating is by means of high frequency electric currents of one or of several turns properly and accurately positioned surrounding the opposed cutting edges 6 and working end or head l of the tool 8. The high frequency current from source 23 generates by electrounagnetic induction heating currents in the steel of the tool to be hardened. Because the irequency of oscillation of the current is high (of the order of 10,900 to several million cycles per second) these currents are generated principally in the skin of the metal. The tool with the cutting edges 8 opposed and opened slightly, so that the opposed edges do not touch to convey leakage currentsfrom one to the other which would cause sparking and pitting oi 'the edges, is positioned within thec'oil; the current is turned'on for a predetermined short time, of the order of a few seconds, after which the tool with the skin and cutting edges heated above the Curie point is allowed to'drop into a quench tank Q oi oil; water, brine-or other medium; as is suitable for the particular steel beinghardened.

'A close predetermined time and power cycle must'be worked out for each size of tool and of steel used. Some steels are shallow hardening in which cases less power and longer time can heat is conducted from the skin into .therinner body of the tool. In deep hardening steels, short time and powers are essential to prevent a too deep penetration of the hardness which leaves little soft, tough metal at the center of the metal and results in breakage of the. tools in use. In extreme high frequencies and high powers applied'ior short times, external quenching may be unimportant since the heat absorbing pow of the cold steel at the center. of the metal mess is sufficient inmany types oi'steel to oh the shallowly heated surface.

1 is a vertical sectional View throughian inductance coil in which is positioned a pair: of pliers with the rest of the View more or lessldiagrammatic and showing a'machine embodying my inven ion and illustrating my process.

Fig. 2 is a horizontal view of the parts seen imrn ediateiy on line '22 of Fig. l.

3 is a horizontal sectional viewon line The drawings herein merely illustrative of machine and-of my process and the specific description is not to be taken as limiting my invention in either of its aspects, but only to give definitene-ss to what is a workable form of my process.

The machine includes a coil 5 composed conveniently of several loops of copper tubing. This coil is'connected to a source 27 of high frequency alternating current commonly of the order "of from 10,000 to several million cycles per second.

Preferably as shown most plainly Fig. 2 the coil is generally rectangular in horizontal cross section so as to let the head or working end 1 of the tool be as closely surrounded as practiany directelectrical contactoi the tool with the The hand-tool ll is'placed in'position'with In the machine as here illustrated the head of the tool is be used, limited mainly by'the speedby which a matter placed into thecoil from below as that is a con venient practical way of positioning the head of the tool within coil and particularly allows for a ready quick release of the tool from its position within the coil seeing that under most conditions the tool remains in the coil only of a few seconds, say three and one-half seconds for a medium size of common pliers with steel'such as S. A. E. 1080. As-

suming then thatthe head of the tool is to be placed into the coil from below, although it will be obvious that that is merely a matter of physical construction of the machine and other equivalent arrangements may be used, the pliers will preferably be held in the relative position shown in Fig. 1 by the following described releasable holding device:

Near the coil there is provided a releasable holding device which in one position as shown in Fig. 3 is adapted to hold the hand tool 8 with its head I in proper position in the coil 5. When the tool head is to be placed into the coil from below a convenient form of this releasable holding device is such as shown in Figs. 1 and 3 wherein the suitably supported pair of movable arms l2 have their opposed inturned ends ll engage the hand too] just below the central pivoted parts thereof. On the opposing inner surfaces of the arms l2 are provided inwardly curved cam faces l4 against the more remote sides of which (relative to the hand tool) impinges a rounding boss l5 projecting from a suitable pivoted lever 16 so that when the solenoid l9 moves the outer end [8 of the lever IE to the left as the device is here arranged, the boss I5 engages the cam surfaces l4 and moves them apart and thereby in an obvious manner separates the inturned ends II and thus the releasable holding device is moved to non-supporting position and the tool is allowed to drop into the quenching tank 20. Obviously other forms of a releasable tool holding device can be provided without departing from the claims herein.

Commonly I provide my machine with some sort of a timing apparatus. The apparatus suggested in Fig. 1 is an electrically operating timer although other forms of timer may be obviously used. The timer illustrated is brought into operation by the starting button 2| being depressed into contact with the contact piece 22. Promptly thereupon the circuit through the alternating current source to the high frequency generator I is completed so as to bring the alternating high frequency current into action upon the coil 5.

After the lapse of the predetermined time and usually only a matter of a few seconds the timer operates to disconnect the source of power and at the same time the current is closed through the wires and 26 leading to the solenoid I9.

' As already suggested this is of such form that on the solenoid being energized its movable core I1 will be drawn to the left and as already mentioned will move the prongs of the holding device and particularly its inturned ends I I away from each other and thus allow the then unsupported tool to drop into the quenching tank 9.

I believe that I am the first to harden the 0pposed cutting edges of jointed hand tools and the thin exterior surface or casing of the head of such tools by induced electric current after the-members of the jointed tool have been assembled. As the cutting edges of a jointed hand tool, for example a pair of pliers, are located closely opposed and close to the center of the head, it has been difiicult if not impossible with ordinary methods of hardening, to harden the cutting edges and a thin outer layer after the parts are assembled without hardening too much of the mass of the head, but with my process I am enabled to easily and regularly accomplish this result because the heating currents that are induced in the head of the tool are limited to a determinable relatively shallow layer or casing along the external surface of the tool. By properly positioning the head of the pliers within the inductance coil and by properly proportioning the time of heating according to the high frequency and power of the inductance coil and considering the metallurgical and chemical character of the steel of the plier and the size of the tool, I am able to effect a heating of the carefully spaced cutting edges and of the desired depth of the casing of the head of an assembled plier so as to secure the proper hardening of the cutting edges and of the casing without disturbing the soft tough character of the mass of the tool head within the shallow outer hardening casmg.

Another advantage of my process used on assembled jointed tools is that by my process the two cutting edges are hardened alike so that neither edge will spoil the other or be spoiled by it.

My invention as described herein is shown as concerned only with the heating and quenching of the tools. It is recognized that nearly all steels hardened by such operations are excessively hard and accordingly too brittle and this has to be corrected by a drawing or tempering operation which consists of reheating the article say from 300 F. to 600.F. and allowing it to C001. No apparatus for such drawing or tempering is shown. That used by me is common to this art.

Furthermore, in thus heat treating two joined cutting members they must be correctly located in the coil and relative to each other so that each member will get its proper amount of heat and will not be shadowed by the other member. Particularly it will be noted that the too1 is placed in the coil with the cutting edges of the tool separated part way so that no induced current will pass from one cutting edge to the other, as, if that happened, the edges would be burned or pitted so that they would be defective and useless.

Again, it may be stated that the too] should be placed in the coil so that both members are in the same position relative to the coil so that they will each receive the same effective induced current or heating effect as each other. I have found that the preferred and most desirable pattern of heat treatment is to have the head of the tool so placed in the coil that the longitudinal axis of the tool will be not only parallel with but preferably coinciding with the longitudinal axis of the coil. This position of the plier in the coil is shown in Fig. 1 and accomplishes the desirable purposes mentioned in this and the next preceding paragraph.

It will be especially noticed that while my process has hardened the desired thin outer casing and the cutting edges of the tool, it has left the core in its previous metallurgical and physical condition, or in other words its hardness has not been increased or decreased.

Therefore I can at will by previous treatment of the tool produce exactly the ultimate character in the core that I want by giving the whole tool that character and then rely upon my process to harden as desired only the thin casing and the cutting edges.

opposed cut ing edges and the irregular outer surface of the head portions of a pair of pliers, said cutting edges facing each other and comprising an integral part of the inside of said head portions, respectively, said pliers comprising at least a first and a second member each having a pivotable body portion connected together by a metalto-metal pivotal connection with each member including said head portion and the cut ing edge thereon extending away from one side of the pivotal connection, said first member having the inner end of its cutting edge integrally terminating with the pivotable body portion thereof and the inner end of the cutting edge of the second member terminating next adjacent to the pivotable body portion of the first member and defining a space therebetween. said inner terminating end of the cutting edge and said pivotable body portion of the first member being movable relative to each other, said members being composed of metal hardenable by heating and quenching, the process of inductively heating the cutting edges and the outer surface of the head portions of the pliers which comprises the steps of positioning the head portions pivotably open to space the cutting edges from each other, providing a coil having an inner surface defining an aperture having a substantially rectangular cross-section which is noncomforming to the irregular shape of said pivotally spaced head portions, said aperture having a cross-sectional area amply large to receive the pivotally spaced head portions with an appreciable and irregular air gap between said head portions and said inner surface, said coil having an entrance end and a terminal end, inserting the movable head portions of the pliers in the aperture with the pivotal connection located near said entrance end and with the cutting edges of the head portions extending in substantially the same general direction as the aXis of the coil, energizing said coil with high frequency current of at least 10.000 cycles per second to thereby establish high frequency magnetic lines of flux extending in the same general direction as the axis of the coil and to establish opposite magnetic poles at the ends of the coil having a distance between the poles greater than the length of the cutting edges, said lines of fiux thereby establishing a heating current which flows about each head por tion and the cutting edge thereon and in a plane substantially perpendicular to the cutting edge, maintaining said head portions in said magnetic field until the cutting edges and the outer surface of the head portions are heated to a hardening temperature, and then removing the head portions from the magnetic field.

2. In the process of inductively hardening the opposed cutting edges and the irregular outer surface of the head portions of a pair of pliers, said cutting edges facing each other and comprising an integral part of the inside of said head portions, respectively, said pliers comprising at least a. first and a second member each having a pivotable body portion connected together by a metalto-metal pivotal connection with each member including said head portion and the cutting edge thereon extending away from one side of the pivotal connection, said first member having the inner end of its cutting edge integrally terminating with the pivotable body portion thereof and the inner end of the cutting edge of the second member terminating next adjacent to the pivotable body portion of the first member and defining a space therebetween, said inner terminating end of the cutting edge and said pivotable body portion of the first member being movable relative to each other, said members being composed of metal hardenable by heating and quenching the process of inductively heating the cutting edges and the outer surface of the head portions of the pliers which comprises the steps of positioning the head portions pivotably open to space the cutting edges from each other, providing a coil having an inner surface defining an aperture which is nonconforming to the irregular shape of said pivotally spaced head portions, said aperture having a cross-sectional area amply large to receive the pivotally spaced head portions with an appreciable and irregular air gap between said head portions and said inner surface, placing the movable head portions of the tool in the aperture of said coil with the pivotal connection located near one end of said coil and with the outer end of the cutting edges of the head portions extending in substantially the same direction as the axis of the coil, energizing said coil with high frequency current of at least 10,000 cycles per second to thereby establish high frequency magnetic lines of flux extending in the same general direction as the axis of the coil and to establish opposite magnetic poles at the ends of the coil having a distance between the poles greater than the length of the cutting edges, maintaining said head portions in said magnetic field until the cutting edges and the outer surface of the head portions are heated to a hardening temperature, and then removing the head portions from the magnetic field.

FALIH N. DARMARA.

REFERENCES CITED The following references are of record in the file of this patent:

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